Sputtering target for forming wiring film of flat panel display

ABSTRACT

A copper alloy wiring film of a flat panel display of the present invention and a sputtering target for forming the same have a composition including Mg: 0.1 to 5 atom %; either one or both of Mn and Al: 0.1 to 11 atom % in total; and Cu and inevitable impurities as the balance, and if necessary, may be further including P: 0.001 to 0.1 atom %.

TECHNICAL FIELD

The present invention relates to a sputtering target capable of farminga wiring film of a flat panel display having a uniform specificelectrical resistance over the whole surface thereof, and a wiring filmof a flat panel display that is formed using the target.

The present application claims priority on Japanese Patent ApplicationNo. 2008-199559 filed on Aug. 1, 2008 and Japanese Patent ApplicationNo. 2009-157493 filed on Jul. 2, 2009, the contents of which areincorporated herein by reference.

BACKGROUND ART

A copper alloy wiring film is used as a wiring film of a flat paneldisplay such as a liquid crystal display, a plasma display, an organicEL display, and an inorganic EL display, and for example, a liquidcrystal display device is known in which a copper alloy wiring filmcontaining 1 to 5 atom % of Mg, and Cu and inevitable impurities as thebalance is formed (see Patent Document 1).

Furthermore, a copper alloy wiring film, which contains either one of 1atom % or less of Al, 0.5 atom % or less of Si, 2 atom % or less of Be,2 atom % or less of Cr, 2 atom % or less of Mg, 0.5 atom % or less ofSn, 4 atom % or less of Zn, and 2 atom % or less of Ce, as an additionelement, is known to have excellent migration resistance. It is alsoknown that the copper alloy wiring film is formed by sputtering using atarget containing the same components as the copper alloy wiring film(see Patent Document 2).

The copper alloy wiring film in the flat panel display is formed on aglass substrate by sputtering, and then the film is subjected to a heattreatment. When the heat treatment is performed, the addition elementincluded in the copper alloy wiring film becomes an oxide and is movedto a front surface and a rear surface of the copper alloy wiring film.Thereby, oxide layers of the addition element are formed in the frontsurface and the rear surface of the copper alloy wiring film. The formedoxide layer of the addition element prevents Si or the like, which is abasic component of the glass substrate, from diffusing and penetratinginto the copper alloy wiring film; and thereby, an increase in theresistivity of the copper alloy wiring film is inhibited. In addition,the formed oxide layer of the addition element improves the adhesionproperty of the copper alloy wiring film relative to the glasssubstrate.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Unexamined Patent Application, FirstPublication No. H09-43628

Patent Document 2: Japanese Unexamined Patent Application, FirstPublication No. H06-97164

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Recently, flat panel displays have become increasingly larger, and largeliquid crystal panels having sizes of 50 inches or more have come to bemass produced. For this reason, the copper alloy wiring film is formedon a wide glass substrate surface by the sputtering. However, in thecopper alloy wiring film formed on the wide glass substrate surface bythe sputtering, the resistivity value (specific electrical resistance)varies from area to area, and this tendency remarkably occurs in thecopper alloy wiring film formed by using a Mg-containing copper alloytarget.

Means for Solving the Problems

Thus, the inventors developed a target formed of Mg-containing copperalloy capable of forming a copper alloy wiring film in which a variationin the resistivity value from area to area is small, and the inventorscarried out research in order to obtain the copper alloy wiring film inthe flat panel display by using the target. As a result, the inventorshave found that a copper alloy thin film, which is obtained bysputtering using a copper alloy target including: pure copper(especially, oxygen-free copper having a purity of 99.99% or more); Mg:0.1 to 5 atom %; and either one or both of Mn and Al: 0.1 to 11 atom% intotal, has a smaller variation in the resistivity value and more uniformresistivity value as a whole than those of a copper alloy thin film ofthe related art which is obtained by sputtering using a copper alloytarget including Mg: 1 to 5 atom %, and Cu and inevitable impurities asthe balance.

The present invention was made based on the above-mentioned researchresults and has the following features.

According to a first embodiment, there is provided a sputtering targetfor forming a wiring of a flat panel display that has a compositionincluding: Mg: 0.1 to 5 atom %; either one or both of Mn and Al: 0.1 to11 atom % in total; and Cu and inevitable impurities as the balance.

According to another embodiment, there is provided a wiring film of aflat panel display consisting of a copper alloy thin film which isobtained by sputtering using the sputtering target described in thefirst embodiment, and has a composition including: Mg: 0.1 to 5 atom %;either one or both of Mn and Al: 0.1 to 11 atom % in total; and Cu andinevitable impurities as the balance.

The copper alloy thin film which configures the wiring of the flat paneldisplay is manufactured by sputtering using the target. The target ismanufactured by, for example, the following manner. At first,oxygen-free copper having a purity of 99.99% or more is melted in ahigh-purity graphite crucible by induction heating under an inert gasatmosphere. Then, Mg at an amount in a range of 0.1 to 5 atom %, andeither one or both of Mn and Al at a total amount in a range of 0.1 to11 atom % are added to the molten copper. The obtained molten metal iscasted and solidified under an inert gas atmosphere. The cast issubjected to hot rolling and stress relief annealing. The copper alloythin film for the flat panel display can be formed by jointing theobtained target to a backing plate and performing sputtering undernormal conditions.

The reasons for limiting the ranges of the component compositions of thesputtering target of the present invention and the copper alloy thinfilm formed using the target as mentioned above will be described.

(a) Component Composition of Target

The reasons for limiting the amount of Mg to be in a range of 0.1 to 5atom % and limiting the total amount of either one or both of Mn and Alto be in a range of 0.1 to 11 atom % which are contained in a target areas follows. In the case where a copper alloy thin film is formed bysputtering using a target which contains Mg: 0.1 to 5 atom % togetherwith either one or both of Mn and Al: 0.1 to 11 atom % in total, avariation in the resistivity value from area to area becomes small. Inthe case where the amount of Mg is in a range of less than 0.1 atom % orthe total amount of either one or both of Mn and Al is in a range ofless than 0.1 atom %, the desired effects are not attained; andtherefore, this case is not preferable. In the case where the amount ofMg is in a range of more than 5 atom % or the total amount of either oneor both of Mn and Al is in a range of more than 11 atom %, a furtherimprovement in desired characteristics is not recognized, and, inaddition, a resistance of the formed copper alloy thin film increases;and therefore, this case is not preferable.

(b) Component Composition of Copper Alloy Thin Film

Mg:

Mg makes grains fine, and Mg suppresses the generation of thermaldefects such as hillocks and voids in a copper alloy thin film whichconfigures a wiring film in a flat panel display. As a result, migrationresistance is improved. In addition, Mg forms a Mg oxide layer on afront surface and a rear surface of the copper alloy thin film during aheat treatment to prevent Si or the like, which is a main component of aglass substrate, from dispersing and penetrating into the copper alloywiring film. As a result, an increase in the resistivity value of thecopper alloy wiring film is prevented, and the adhesion property of thecopper alloy wiring film to the glass substrate is also improved. In thecase where the amount of Mg is in a range of less than 0.1 atom %,desired effects are not attained; and therefore, this case is notpreferable. In the case where the amount of Mg is in a range of morethan 5 atom %, an improvement in the property is not recognized, and inaddition, the resistivity value is increased; and thereby, a suitablefunction as the wiring film is not exhibited. Therefore, this case isnot preferable. Thus, the amount of Mg contained in the copper alloythin film is set to be in a range of 0.1 to 5 atom %.

Mn and Al:

By containing these components along with Mg, a multiple oxide or anoxide solid solution which includes Mg with Mn and/or Al is formed inthe front surface and the rear surface of the copper alloy thin film;and thereby, the adhesion property to the surface of the glass substrateis further improved. Furthermore, since an oxide which is formed in thefront surface and the rear surface of the copper alloy thin filmcontains the multiple oxide or the oxide solid solution which includesMg with Mn and/or Al having high chemical stability, the chemicalstability of the copper alloy wiring is improved. In the case whereeither one or both of these components are added at a total amount in arange of less than 0.1 atom %, the effect of improving the adhesionproperty cannot be obtained; and therefore, this case is not preferable.In the case where Mn and Al are added at an amount in a range of morethan 11 atom % in total, an improvement in the property is notrecognized, and in addition, the resistivity value of the wiring filmincreases; and therefore, this case is not preferable.

P:

A small amount of P facilitates the casting property of a copper alloywithout deteriorating the properties such as the resistivity, thehillocks, the voids and the adhesion property required for the copperalloy thin film; and therefore, P is added as necessary. However, in thecase where P is added at an amount in a range of less than 0.001 atom %,there is no effect thereof. In the case where P is added at an amount ina range of more than 0.1 atom %, there is no improvement in the castingproperty. Thus, the amount of P is set to be in a range of 0.001 to 0.1atom %.

Effects of the Invention

In the case where a copper alloy thin film is formed by sputtering usingthe target of the present invention, even if a glass substrate becomeslarger, a variation in the resistivity value from area to area in theformed copper alloy thin film is small. In addition, the adhesionproperty to the glass substrate surface is improved, and the resistivityvalue is low. Therefore, it is possible to form a copper alloy wiringfilm of a high-definition and large flat panel display.

BEST MODE FOR CARRYING OUT THE INVENTION

Oxygen-free copper having a purity of 99.99 mass % was prepared, and theoxygen-free copper was melted in a high-purity graphite crucible byinduction heating under an Ar gas atmosphere. Mg, Mn and Al were addedto the obtained molten copper, and P was added as necessary. Thesemetals were melted, and the composition thereof was adjusted so as toobtain molten metals having the component compositions shown in Table 1.The obtained molten metals were casted by a cooled carbon mold. Thecasts were subjected to hot rolling and stress relief annealing. Thesurfaces of the obtained rolled products were processed by a lathe toproduce copper alloy sputtering targets of the present invention(hereinafter, referred to as targets of the present invention) 1 to 25,comparison copper alloy sputtering targets (hereinafter, referred to ascomparison targets) 1 to 4, and a sputtering target of the related art(hereinafter, referred to as a target of the related art) 1 which had acircular plate shape and a size of an outer diameter: 200mm×a thickness:10 mm and the component compositions shown in Table 1.

Backing plates formed of oxygen-free copper were prepared, and each ofthe targets of the present invention 1 to 25, the comparison targets 1to 4, and the target of the related art 1 was overlapped with thebacking plate formed of oxygen-free copper, and was soldered by indiumat 200° C.; and thereby, each of the targets of the present invention 1to 25, the comparison targets 1 to 4, and the target of the related art1 was jointed to the backing plate formed of oxygen-free copper toproduce the backing plate target.

The backing plate target obtained by soldering each of the targets ofthe present invention 1 to 25, the comparison targets 1 to 4, and thetarget of the related art 1 to the backing plate formed of oxygen-freecopper was disposed such that a distance between the target and a glasssubstrate (a glass substrate 1737 produced by Corning Company havingsizes of diameter: 200 mm and thickness: 0.7 mm) became 70 mm.

Copper alloy wiring thin films of the present invention (hereinafter,referred to as wiring thin films of the present invention) 1 to 25,comparison copper alloy wiring thin films (hereinafter, referred tocomparison wiring thin films) 1 to 4, and a copper alloy wiring thinfilm of the related art (hereinafter, referred to as a wiring thin filmof the related art) 1 were formed on surfaces of the glass substratesunder the following conditions:

power supply: direct current;

sputter power: 600 W;

an attained degree of vacuum: 4×10⁻⁵ Pa;

atmosphere gas composition: a mixture gas of Ar: 90 volume % and oxygen:10 volume %;

a gas pressure: 0.2Pa; and

a glass substrate heating temperature: 150° C.

The copper alloy wiring thin films had a circular shape, a diameter of100 mm, a thickness of 300nm, and component compositions shown in Tables2 and 3. The obtained wiring thin films of the present invention 1 to25, the comparison wiring thin films 1 to 4 and the wiring thin film ofthe related art 1 were charged in a heating furnace, respectively, andwere subjected to a heat treatment in an Ar atmosphere under conditionswhere the temperature rising rate was 5° C./min, the maximum temperaturewas 350° C., and the holding time was 30 minutes. With regard to each ofthe obtained circular wiring thin films of the present invention 1 to25, the obtained circular comparison wiring thin films 1 to 4 and theobtained circular wiring thin film of the related art 1, theresistivities were measured by a four probe method at the center, at apoint distant from the center by 50 mm and at a point distant from thecenter by 100 mm, and the difference between the maximum value and theminimum value was obtained. The results are shown in Tables 2 and 3, andthe variation in the resistivity value of the wiring thin film wasevaluated.

In addition, a cross-cut adhesion test was performed in accordance withJIS-K5400 as follows. Equally spaced cut lines were made at 1 mmintervals in a grid arrangement in each of the wiring thin films of thepresent invention 1 to 25, the comparison wiring thin films 1 to 4 andthe wiring thin film of the related art 1. Then, a scotch tapemanufactured by 3M Company was put on the surface of the wiring thinfilm and was peeled off. Thereafter, an area ratio (area%) of the wiringthin film remained to adhere to the glass substrate within a10-mm-square in a center portion of the glass substrate was measured.The results are shown in Tables 2 and 3, and the adhesion properties tothe glass substrate, of the wiring thin film of the present invention 1to 25, the comparison wiring thin films 1 to 4 and the wiring thin filmof the related art 1, were evaluated.

With regard to the wiring thin films of the present invention 1 to 25,the comparison wiring thin films 1 to 4 and the wiring thin film of therelated art 1 which had been subjected to the heat treatment, fiveportions in each surface thereof were observed by a SEM at amagnification of 5,000, and it was observed whether or not hillocks andvoids were generated. The results are shown in Tables 2 and 3.

TABLE 1 Component composition (atom %) Cu and inevitable Target Mg Mn AlP impurities Present 1 0.1 9.8 — — balance invention 2 0.5 1.0 — —balance 3 0.9 7.3 — — balance 4 1.4 3.0 — — balance 5 1.8 4.3 — —balance 6 2.6 5.0 — — balance 7 3.0 3.3 — — balance 8 4.2 0.1 — —balance 9 4.9 1.9 — — balance 10 0.1 — 3.0 — balance 11 0.5 — 9.9 —balance 12 1.0 — 2.2 — balance 13 1.4 — 6.2 — balance 14 2.0 — 4.3 —balance 15 2.6 — 5.3 — balance 16 2.7 — 0.1 — balance 17 0.5 0.2 0.8 —balance 18 5.0 0.5 1.6 — balance 19 2.0 2.1 2.1 — balance 20 3.9 2.1 6.4— balance 21 0.5 0.2 0.9 0.001 balance 22 5.0 0.5 1.5 0.05 balance 233.9 2.1 6.0 0.1 balance 24 2.1 — 8.3 — balance 25 4.0 — 11.0 — balanceComparison 1 0.05* 0.05* — — balance 2 0.05* — 0.05* — balance 3 5.7*11.0* 0.05* — balance 4 5.7* 5.0* 10.5* — balance Relate art 1 3.5 —* —*— balance *signs show values out of the ranges of the present invention.

TABLE 2 Cross-cut Measured resistivity values adhesion test of wiringthin film (μ Ωcm) Ratio of Component composition of Difference Presencewiring thin wiring thin film (atom %) 50 100 between of film adhered Cuand mm mm maximum hillocks to glass Wiring thin Used target inevitablefrom from and and substrate film of Table 1 Mg Mn Al P impurities Centercenter center minimum voids (area %) Present 1 Present 1 0.1 7.5 — —balance 12.6 12.5 12.7 0.2 none 100 invention 2 invention 2 0.4 0.9 — —balance 3.1 3.1 3.2 0.1 none 100 3 3 0.8 6.0 — — balance 10.9 10.8 10.80.1 none 100 4 4 1.1 2.3 — — balance 5.4 5.4 5.4 0.0 none 100 5 5 1.43.7 — — balance 7.8 7.8 7.5 0.3 none 100 6 6 2.1 4.3 — — balance 8.5 8.78.8 0.3 none 100 7 7 2.5 2.9 — — balance 6.8 6.7 6.8 0.1 none 100 8 83.6 0.1 — — balance 3.0 2.9 3.1 0.2 none 100 9 9 3.9 1.6 — — balance 5.35.3 5.1 0.2 none 100 10 10 0.1 — 2.3 — balance 3.1 3.2 3.1 0.1 none 10011 11 0.4 — 7.3 — balance 5.2 5.1 5.3 0.2 none 100 12 12 0.8 — 1.9 —balance 3.0 3.1 3.0 0.1 none 100 13 13 1.2 — 4.5 — balance 4.5 4.5 4.40.1 none 100 14 14 1.8 — 3.2 — balance 4.0 4.0 4.1 0.1 none 100 15 152.1 — 3.8 — balance 4.5 4.4 4.4 0.0 none 100

TABLE 3 Cross-cut adhesion test Measured resistivity values Ratio of ofwiring thin film (μ Ωcm) wiring Component composition of DifferencePresence thin film wiring thin film (atom %) 50 100 between of adheredCu and mm mm maximum hillocks to glass Wiring thin Used target ofinevitable from from and and substrate film Table 1 Mg Mn Al Pimpurities Center center center minimum voids (area %) Present 16Present 16 2.4 — 0.1 — balance 2.6 2.6 2.6 0.0 none 100 Invention 17Invention 17 0.4 0.2 0.6 — balance 2.6 2.6 2.5 0.0 none 100 18 18 4.20.3 1.3 — balance 4.2 4.2 4.2 0.0 none 100 19 19 1.7 1.7 1.5 — balance5.7 5.7 5.7 0.0 none 100 20 20 2.9 1.7 4.8 — balance 7.7 7.5 7.7 0.2none 100 21 21 0.4 0.2 0.6 0.001 balance 2.6 2.6 2.6 0.0 none 100 22 223.9 0.4 1.2 0.04 balance 4.3 4.3 4.4 0.1 none 100 23 23 3.2 1.7 4.6 0.1balance 8.0 7.7 7.7 0.3 none 100 24 24 1.9 — 7.5 — balance 5.7 5.8 5.60.2 none 100 25 25 3.2 — 9.1 — balance 6.4 6.5 6.3 0.2 none 100Comparison 1 Comparison 1 0.04* 0.04* — — balance 2.0 2.0 2.0 0.0present 79 2 2 0.04* — 0.04* — balance 1.9 2.0 2.0 0.1 present 41 3 35.1* 10.1* 0.04* — balance 16.4 16.5 16.9 0.5 none 100 4 4 5.2* 4.4 9.2— balance 14.6 14.7 15.0 0.4 none 100 Related Art 1 Related Art 1 2.9 —*—* — balance 2.7 3.0 .3.7 1.0 none 59 *signs show values out of theranges of the present invention.

The following can be understood from the results shown in Tables 1 to 3.

(i) With regard to the wiring thin film of the related art 1 which wasformed by sputtering using the target of the related art 1 solelycontaining Mg with Cu, a difference in resisitivity between the centerportion and the peripheral portion is large, and the adhesion propertyto the glass substrate is poor. In contrast, with regard to the wiringthin films of the present invention 1 to 25 which contained Mg togetherwith either one or both of Mn and Al, the differences in resistivitybetween the center portion and the peripheral portion are small; andtherefore, the variations in the resistivity value are small. Inaddition, the adhesion properties to the glass substrate are excellent.

(ii) With regard to the comparison wiring thin film 1 which was formedby sputtering using the comparison target 1 containing Mg and Mn atamounts lower than the ranges of the present invention, and thecomparison wiring thin film 2 which was formed by sputtering using thecomparison target 2 containing Mg and Al at amounts lower than theranges of the present invention, the adhesion properties are poor.Furthermore, hillocks and voids are generated. Therefore, migration mayeasily occur, which is not desirable. Moreover, with regard to thecomparison wiring thin films 3 and 4 of which the Mg amount and thetotal amount of Mn and Al are higher than the ranges of the presentinvention, the resistivities becomes too large; and therefore, thesefilms are not desirable as the wiring thin film.

1-4. (canceled)
 5. A sputtering target for forming a wiring film of aflat panel display having a composition consisting of: Mg: 0.1 to 5 atom%; Al: 0.8 to 11 atom %; and the balance of Cu and inevitableimpurities.
 6. A sputtering target for forming a wiring film of a flatpanel display having a composition consisting of: Mg: 0.1 to 5 atom %;Al: 0.8 to 11 atom %; P: 0.001 to 0.1 atom%; and the balance of Cu andinevitable impurities.
 7. A sputtering target for forming a wiring filmof a flat panel display having a composition consisting of: Mg: 0.1 to 5atom %; Al: 0.8 to 11 atom %; Mn; and the balance of Cu and inevitableimpurities. wherein a total content of Mn and Al is in a range of morethan 0.8 to 11 atom %.
 8. A sputtering target for forming a wiring filmof a flat panel display having a composition consisting of: Mg: 0.1 to 5atom%; Al: 0.8 to 11 atom %; P: 0.001 to 0.1 atom%; Mn; and the balanceof Cu and inevitable impurities. wherein a total content of Mn and Al isin a range of more than 0.8 to 11 atom %.